1. Field of the Invention
The present invention relates to a temperature predicting or estimating system for an internal combustion engine, which monitors a portion of the engine where a temperature varies depending on an operating condition of the engine, e.g. a catalytic converter or catalyst and an exhaust pipe, so as to predict or estimate the temperature thereof. The present invention further relates to a temperature control system for the engine, including the foregoing temperature predicting system.
2. Description of the Prior Art
As is well known in the art, three way catalytic converters have been widely used in internal combustion engines installed on vehicles to remove harmful gas components from engine exhaust.
In general, the three way catalytic converter should be operated in a high-temperature range to effectively remove the harmful gas components. On the other hand, excessively high temperatures tend to lower the purification efficiency of the catalytic converter, and also to reduce the durability of the catalytic converter catalyst.
Under the circumstances, Japanese First (unexamined) Patent Publication No. 60-101241, for example, discloses monitoring temperature of the exhaust by an appropriate temperature sensor and maintaining the temperature within a given target range by controlling the amount of fuel supplied to the engine and one ignition timing of the engine. As appreciated, when the fuel supply is increased, an air-fuel ratio becomes richer so as to lower the exhaust gas temperature. Similarly, when the ignition timing of the engine is advanced to a greater extent, the exhaust gas temperature is lowered.
Accordingly, on a theoretical basis, it certainly appears that the exhaust gas temperature can be maintained within the given target temperature range and prevented from getting excessively high by measuring the exhaust gas temperature using the temperature sensor and by controlling the fuel supply amount to the engine and the ignition timing of the engine based on the measured temperature.
However, temperature sensors normally have non-ideal response characteristics. Particularly, the relatively low-priced temperature sensors employed in mass-produced vehicles tend to have significant response delays. This results in a large difference between a temperature of the exhaust gas measured by the temperature sensor and an actual temperature of the exhaust gas. Due to this deviation, the exhaust gas temperature can not be accurately controlled so that, for example, a temperature within the foregoing three way catalytic converter can not be controlled, either.
Although the measurement of the exhaust gas temperature has been referred to in the foregoing description, the same discussion applies with regard to measuring temperatures of other engine portions which change their temperature depending on the engine operating conditions, using the temperature sensors.